Characterization of endogenous carrier-mediated taurocholate efflux from Xenopus laevis oocytes.

Taurocholate efflux was studied in Xenopus laevis oocytes and is consistent with a carrier-mediated process. This carrier can be competitively inhibited and trans stimulated by glycocholate. Transport is also trans stimulated by taurochenodeoxycholate and S-hexylglutathione, but not taurolithocholate or daunomycin, reflecting a range of specificity including substrates of both the hepatic canalicular bile acid transporter and the multispecific organic anion transporter. In addition, ATP added to the outside of the oocyte results in an increase in the maximal velocity of this transport process. The physiologic function of this endogenous carrier is not known, but it may act as a generalized system for the efflux of potentially toxic organic anions.